1. Field of the Invention
This invention relates to the protection of dentures against the accumulation of denture plaque.
2. Description of Prior Art
It is important that denture wearers keep their dentures free from the accumulation of bacteria and their products. This is important not only from the appearance point of view (dentures having an accumulation of plaque tend to have a stained appearance) but also from the medical point of view. If dentures are not maintained adequately free from plaque material, infection may occur. This is particularly the case for the palatal-contacting surface of the denture plate since plaque accumulation frequently results in denture stomatitis, which has been estimated to affect up to 40% of denture wearers. Furthermore, accumulation of denture plaque predisposes the wearer to periodontal diseases and has been thought to give rise to infection of the dentures by Candida.
There are currently two widely used methods of removing plaque accumulation from dentures. According to the first of these, the plaque is removed chemically by use of oxidising or bleaching agents. Thus the dentures may be soaked in oxidising or bleaching agent overnight. However the use of such strong chemicals nightly over prolonged periods tends to lead to a deterioration in the dentures. Alternatively dentures are kept clean by scrubbing, generally using an abrasive agent. However again this is a cleansing method which causes deterioration in the dentures themselves.
Attempts have been made to prevent the accumulation of denture plaque within the mouth by the use of bactericidal or bacteristatic treatments in the form of rinses and mouthwashes. However the use of such bactericidal or bacteristatic formulations in the buccal cavity can lead to the selection and ultimate preponderance of resistant bacterial species which will make the formulations ineffective. The development of resistant flora is a well-known side-effect associated with the use of chemical antibacterial agents. Exposure of oral bacterial to antiseptics such as chlorhexidine can also lead to the development of resistance to these agents. In addition, the use of chemical antibacterial agents raises problems of toxicity and unwelcome side effects. In the case of chlorhexidine, for example, staining of the teeth is very common (occuring in approximately 50% of patients) and staining of the tongue has been reported. Also, using rinses and mouthwashes in this way, it is difficult to maintain an adequate concentration at the site of bacterial accumulation and thus the treatment method tends to be both wasteful and ineffective.
E. Budtz-Joergensen and S. Kaaber, Scandinavian Journal of Dental Research 94, 568-574 (1986) have suggested coating the denture with a surface glaze of a cross-linked acrylic polymer. The dentures are coated with a polyfunctional acrylic monomer mixed with a diluent and an initiator and the mixture is cured by exposure to UV light for 20 minutes. This method is claimed to reduce accumulation of plaque, but the method of coating is inconvenient and the coating cannot be renewed.
U.S. Pat. Nos. 4,360,514, 4,360,515, 4,361,547, 4,362,712, 4,364,927 and 4,403,089assigned to Johnson & Johnson, propose the use of carboxylated or sulphonated aromatic formaldehyde condensation polymers and sulphonated alkylnaphthalenes to prevent accumulation of plague on teeth. These inventions are based on the hypothesis that these strongly anionically charged polymers deposited on the teeth repel negatively charged microorganisms responsible for generating plaque. While these patents are primarily concerned with teeth, it is mentioned that these agents can be included in denture cleansers. It is doubtful, however, whether such compounds would be approved for oral use.
It has, therefore, been a problem to find an alternative method of protecting dentures against accumulation of plaque.
Further prior art is discussed below after "Summary of the Invention", without which its context would not be apparent.